1. FIELD OF THE INVENTION
This invention relates to a planographic master plate which can be used for offset printing without using dampening water.
2. DESCRIPTION OF THE PRIOR ART
As is well known, conventional planographic printing plates consist of an image area (oleophilic portion) which is hard to wet with water and which receives only printing ink, and a non-image area (hydrophilic portion) which is easily wetted with water but repels printing ink, both of which areas are on the same surface of a plate-making substrate. In such planographic plates, the non-image area is rendered hydrophilic by etching and the ink repellency thereof is maintained by applying dampening water thereto during printing. Because of the use of dampening water, these planographic master plates have various defects, among which are:
(1) The ink is liable to be emulsified. PA1 (2) Drying of the ink is slow. PA1 (3) The printed colors and gloss worsen with time, PA1 (4) The durability of the plate in printing is insufficient. PA1 (5) A complicated printing press must be used. PA1 (6) Because of the etching treatment required, plate making is complicated.
In an attempt to remedy these defects of planographic master plates, recently developed planographic printing methods do not require dampening water or an etching treatment as a result of utilizing the superior ink-repelling property of silicones. However, these planographic master plates which do not require dampening water have not found a wide range of applicability, as they depend on the method of plate-making and processes for making such plates is limited. For example, when an ink-receptive image area is formed on such a master plate by an electrophotographic plate-making process or by a direct image process involving direct writing or drawing by, for example, a typewriter, both of which processes have recently gained widespread acceptance in the printing industry as simple plate-making techniques, the toner image or direct writing images cannot be firmly bonded to the silicone layer, and, therefore, the resulting printing plate has poor durability in printing.